Your opinions, please...

The 8" f/6 is not too slow for deep sky objects. In fact, it is perfect and
the tube is not really that long. You want a 5mm to 6mm exit pupil which
translates to a 30mm to 35mm focal length eyepiece. I would suggest 2-inch
eyepieces for wide fields and there are several reasonably priced selections
on the market. The classical 7mm exit pupil is too big but even that is in
reach with a 40mm eyepiece.

A big advantage of f/6 is that you can get by without a coma corrector. At
f/5 or faster you have to start thinking about buying a corrector. Stay
away from the f/3.5! Way too much coma and it will not correct well with a
coma corrector.

Del Johnson




"Alan W. Craft" wrote in message
...

I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too
slow for DSO's and the like(not to mention
the tube length), I've looked into the
possibility of an 8" f5 custom-made by
Parks and sold via Scope City...


Alan

Alan W. Craft wrote in message . ..
I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too
slow for DSO's and the like(not to mention
the tube length), I've looked into the
possibility of an 8" f5 custom-made by
Parks and sold via Scope City...

"Thank you for contacting Scope City.
I have reviewed your request for
information on the Parks Optical tube
for telescopes. Based on the information
provided ( 8 inch - f/5 - F=1000, Newtonian)
you would need a 9 3/8th ID 9 3/4 OD
diameter tube, all we need to know from
you is the length you would like to purchase.
You can see a complete listing of all the
tubes Parks offers. We have many in
stock, custom order usually take a
few months."

"...the length I would like to purchase."?

Wouldn't the focal ratio determine that,
or am I missing something?

Substantially, yes, but I suppose you might want a bit longer tube
to cut down on stray light or drop the primary down a bit for some
close-to-the-tube focuser/smaller diagonal combination.


Also, please comment on the focal
ratio I've indicated...advantages...
disadvantages?

All opinions, good or bad, are most
welcome.

Alan

Like some others have said, there's nothing really wrong with an f/6
for most DSOs, IMO. FWIW.

Regards,
Russell

I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too

Hi:

Well...Parks has made some nice optics over the years--if sometimes not as good
as you'd expect--but...you know, lots of Synta and Guan Sheng 8 inch f/5s are
testing out at 1/8 wave...and you can get a whole OTA for a song.

Just a thought...

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

On 24 Jul 2003 21:36:43 GMT, (Rod Mollise) ...reflected:

I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too

Hi:

Well...Parks has made some nice optics over the years--if sometimes not as good
as you'd expect--but...you know, lots of Synta and Guan Sheng 8 inch f/5s are
testing out at 1/8 wave...and you can get a whole OTA for a song.

Just a thought...

I'm intrigued. I went and looked at the "Skywatcher" 's,
and will look again, but I couldn't be assured of receiving
a primary and secondary of such a tolerance, not to
mention the Parks-like tube and component qualities.

But, no, I really couldn't count on that mirror tolerance
with Parks, either.

Also, and perhaps a minor point, the Parks mirrors are of
Pyrex. I didn't see that the Synta's were, but I didn't
research them extensively...yet.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

Alan

On 24 Jul 2003 12:23:57 -0700, (Russell Martin) ...reflected:

Alan W. Craft wrote in message . ..
I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too
slow for DSO's and the like(not to mention
the tube length), I've looked into the
possibility of an 8" f5 custom-made by
Parks and sold via Scope City...

"Thank you for contacting Scope City.
I have reviewed your request for
information on the Parks Optical tube
for telescopes. Based on the information
provided ( 8 inch - f/5 - F=1000, Newtonian)
you would need a 9 3/8th ID 9 3/4 OD
diameter tube, all we need to know from
you is the length you would like to purchase.
You can see a complete listing of all the
tubes Parks offers. We have many in
stock, custom order usually take a
few months."

"...the length I would like to purchase."?

Wouldn't the focal ratio determine that,
or am I missing something?

Substantially, yes, but I suppose you might want a bit longer tube
to cut down on stray light or drop the primary down a bit for some
close-to-the-tube focuser/smaller diagonal combination.

Are you suggesting a "low-profile" or helical focusser?

Though, I didn't understand what you meant when you wrote,
"drop the primary down a bit."

In any case, I would want the telescope to be arranged
and constructed just like the readily-available ones, but an f5
instead of an f6.

Also, please comment on the focal
ratio I've indicated...advantages...
disadvantages?

All opinions, good or bad, are most
welcome.

Alan

Like some others have said, there's nothing really wrong with an f/6
for most DSOs, IMO. FWIW.

I have this "brain cramp" that keeps telling me that you
need low, and even very low, magnification to see most
DSO's, but that's not necessarily true, is it?

Of course, you wouldn't want to use a 5mm on a galaxy.

Regards,
Russell

Alan

Alan W. Craft wrote:
I have this "brain cramp" that keeps telling me that you
need low, and even very low, magnification to see most
DSO's, but that's not necessarily true, is it?

No, indeed it's not. For very small DSOs, you will often want to use
higher magnification.

Of course, you wouldn't want to use a 5mm on a galaxy.

I think there is no "of course" about it. I often want to use a 5 mm
on a galaxy in my 70 mm Ranger. That kind of an eyepiece would only give
me about 96x, typically yielding about a 1/2-degree true field of view,
and nicely framing many DSOs.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

On Thu, 24 Jul 2003 14:14:36 GMT, "Del Johnson" ...reflected:

The 8" f/6 is not too slow for deep sky objects. In fact, it is perfect and
the tube is not really that long.

I agree, and would LOVE to have the 8" f6, but
wouldn't the tube overwhelm a GP-DX mount, let
alone a standard GP? As it is, I'm thinking that
the f5 would be a bit cumbersome in its own
right, but certainly less than the f6.

I've seen the pictures. Parks places the 8" f6
on either their 'Precision,' or, more appropriately,
on their 'Superior' equatorial mounting, and not
at all onto their 'Astrolight' which bears enough
of a resemblance to either the GP or GP-DX
as to preclude their collective considerations.

You want a 5mm to 6mm exit pupil which
translates to a 30mm to 35mm focal length eyepiece. I would suggest 2-inch
eyepieces for wide fields and there are several reasonably priced selections
on the market. The classical 7mm exit pupil is too big but even that is in
reach with a 40mm eyepiece.

A big advantage of f/6 is that you can get by without a coma corrector. At
f/5 or faster you have to start thinking about buying a corrector. Stay
away from the f/3.5!

I'll take that advice, but I'm SOOOOOOOOOO
leaning towards that 8" f5. It would be, perhaps,
the ideal compromise between an f3.5 and an f6.

Way too much coma and it will not correct well with a
coma corrector.

Del Johnson

Thank you, Del.

Alan

You are correct in that an 8" reflector is too much telescope for any GP
mount. I would not go down that road myself. Consider instead a far
superior driven Dob solution.

Del Johnson



"Alan W. Craft" wrote in message
...
On Thu, 24 Jul 2003 14:14:36 GMT, "Del Johnson"
....reflected:

The 8" f/6 is not too slow for deep sky objects. In fact, it is perfect
and
the tube is not really that long.

I agree, and would LOVE to have the 8" f6, but
wouldn't the tube overwhelm a GP-DX mount, let
alone a standard GP? As it is, I'm thinking that
the f5 would be a bit cumbersome in its own
right, but certainly less than the f6.

I've seen the pictures. Parks places the 8" f6
on either their 'Precision,' or, more appropriately,
on their 'Superior' equatorial mounting, and not
at all onto their 'Astrolight' which bears enough
of a resemblance to either the GP or GP-DX
as to preclude their collective considerations.


Alan

On Sat, 26 Jul 2003 18:34:27 GMT, "Del Johnson" ...reflected:

You are correct in that an 8" reflector is too much telescope for any GP
mount. I would not go down that road myself. Consider instead a far
superior driven Dob solution.

Celestron, Orion, Skywatcher, et al are placing 8" f/5's
on Chinese GP-copies. Of course, that's Celestron and Orion.
Also, Meade doesn't seem to be above doing that sort of thing
themselves, thus...

Who am I to be so stringent?

8^)

Dobsonians are attractive, but at this point not as attractive
as equatorially-mounted alternatives, as cost is a factor in my
decisions, but not primarily so.

Del Johnson



"Alan W. Craft" wrote in message
.. .
On Thu, 24 Jul 2003 14:14:36 GMT, "Del Johnson"
...reflected:

The 8" f/6 is not too slow for deep sky objects. In fact, it is perfect
and
the tube is not really that long.

I agree, and would LOVE to have the 8" f6, but
wouldn't the tube overwhelm a GP-DX mount, let
alone a standard GP? As it is, I'm thinking that
the f5 would be a bit cumbersome in its own
right, but certainly less than the f6.

I've seen the pictures. Parks places the 8" f6
on either their 'Precision,' or, more appropriately,
on their 'Superior' equatorial mounting, and not
at all onto their 'Astrolight' which bears enough
of a resemblance to either the GP or GP-DX
as to preclude their collective considerations.

Alan

These companies are only interested in selling telescopes and thus will slap
together anything that sells. You are the one who has to live with the
result. The mount should be the strongest and often the most expensive part
of the total system. It is a common mistake to put all of one's resources
into the telescope tube assembly and then buy some flimsy mount that can't
do the job.

You can buy a good Dobsonian now and add a drive to it later on. Suffice to
say that I used to use an 8" reflector on a GEM (a heavy duty Cave mount)
but now I use a driven Dob with far better results.

Del Johnson



"Alan W. Craft" wrote in message
...
On Sat, 26 Jul 2003 18:34:27 GMT, "Del Johnson"
....reflected:

You are correct in that an 8" reflector is too much telescope for any GP
mount. I would not go down that road myself. Consider instead a far
superior driven Dob solution.

Celestron, Orion, Skywatcher, et al are placing 8" f/5's
on Chinese GP-copies. Of course, that's Celestron and Orion.
Also, Meade doesn't seem to be above doing that sort of thing
themselves, thus...

Who am I to be so stringent?

8^)

Dobsonians are attractive, but at this point not as attractive
as equatorially-mounted alternatives, as cost is a factor in my
decisions, but not primarily so.

Del Johnson



"Alan W. Craft" wrote in message
.. .
On Thu, 24 Jul 2003 14:14:36 GMT, "Del Johnson"
...reflected:

The 8" f/6 is not too slow for deep sky objects. In fact, it is
perfect
and
the tube is not really that long.

I agree, and would LOVE to have the 8" f6, but
wouldn't the tube overwhelm a GP-DX mount, let
alone a standard GP? As it is, I'm thinking that
the f5 would be a bit cumbersome in its own
right, but certainly less than the f6.

I've seen the pictures. Parks places the 8" f6
on either their 'Precision,' or, more appropriately,
on their 'Superior' equatorial mounting, and not
at all onto their 'Astrolight' which bears enough
of a resemblance to either the GP or GP-DX
as to preclude their collective considerations.

Alan